Dragable mask? or a different method?

Can someone point me in the direction of creating this type of draggable mask:
http://www.flashlight.hpg.ig.com.br/photos/pfx1_1i.htm

I know how to make a mask, and how to create a mask with actionscript that moves over an image but how would I create the bar (vertical) that can be dragged over the image(s) to create the mask?

I’ve tried the magnifying glass tutorial but I can’t get the vertical bar to be the mask and draggable.

rberry88